1. Field of the Invention
The present invention relates to a dynamo-electric machine.
2. Description of Related Art
In some dynamo-electric machines (e.g., electric motors), an opening of a cup shaped yoke housing is closed by an end housing or a gear housing. For instance, Japanese Unexamined Patent Publication No. 2008-092641A teaches a geared motor that has a cup-shaped yoke housing. Two permanent magnets are fixed to an inner peripheral surface of the yoke housing with aid of two U-shaped spacer springs (fixation springs), each of which is circumferentially positioned between the magnets to circumferentially exert a resilient force against the magnets. An armature is rotatably received in the yoke housing at a location radially inward of the magnets. A gear housing receives a speed reducing gear mechanism, which reduces a speed of rotation transmitted from a rotatable shaft of the armature. The gear housing is fixed to the yoke housing with a plurality of screws. In such an instance, the screws are required to fix the gear housing to the yoke housing, so that the number of components is disadvantageously increased.
In other types of dynamo-electric machines, a casing includes a yoke housing, which is configured into a generally cylindrical tubular body and receives an armature therein at a location radially inward of permanent magnets fixed to an inner peripheral surface of the yoke housing. An opening of the yoke housing is closed with an end housing. The end housing is fixed to the yoke housing by, for example, staking or crimping (i.e., bending of a metal part of one of the yoke housing and the end housing against the other one of the yoke housing and the end housing to secure therebetween) or a snap-fitting without requiring dedicated screws for fixing therebetween.
In the case where the yoke housing and the end housing are assembled together by the staking or crimping, a dedicated jig (device) needs to be provided, and the assembling process may tend to take a longer time.
In the case where the yoke housing and the end housing are fixed together by the snap-fitting, engaging protrusions of the end housing, which radially inwardly protrude, may be snap-fitted into holes of the yoke housing, which are formed in a peripheral wall of the yoke housing (see, for example, Japanese Unexamined Patent Publication No. 2008-099523A). In such a case, it is possible to eliminate the need for the dedicated jig in comparison to the case where the yoke housing and the end housing are fixed together by the staking. Furthermore, it is possible to eliminate the process of the staking at the assembling process, so that the assembling of the yoke housing and the end housing by the snap-fitting can be more easily performed in comparison to the staking.
However, in the case of assembling the yoke housing and the end housing (housing portions) by the snap-fitting, the holes and the engaging protrusions are formed with certain dimensional tolerances to reliably engage between the holes and the engaging protrusions. Therefore, due to the presence of the dimensional tolerances (play), there is a possibility of moving one of the yoke housing and the end housing relative to the other one of the yoke housing and the end housing in the axial direction to cause rattling movement thereof, thereby generating noisy sound at the connection between the yoke housing and the end housing. Particularly, when the dynamo-electric machine is a blower motor of an air conditioning system, which is placed in a passenger compartment of the vehicle, such a noisy sound annoys passengers of the vehicle.